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LibWeb: Make setInterval() reuse the timer to reduce drift

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Instead of creating a new single-shot timer every time a setInterval
timer reschedules itself, we now use a repeating Core::Timer internally.

This dramatically reduces timer drift, since the next timeout is now
based on when the timer fired, rather than when the timer callback
completed (which could take arbitrarily long since we run JS).

It's not perfect, but it's a huge improvement and allows us to play
DiabloWeb at full framerate (20 fps).
This commit is contained in:
Andreas Kling 2025-12-01 15:23:27 +01:00 • committed by Andreas Kling
parent fb9286eccb
commit 4d27e9aa5e
Notes: github-actions[bot] 2025-12-01 19:00:05 +00:00
4 changed files with 39 additions and 19 deletions
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22
Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp
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@ -37,6 +37,7 @@
#include <LibWeb/HTML/Timer.h>
#include <LibWeb/HTML/Window.h>
#include <LibWeb/HTML/WindowOrWorkerGlobalScope.h>
#include <LibWeb/HTML/WorkerGlobalScope.h>
#include <LibWeb/HighResolutionTime/Performance.h>
#include <LibWeb/HighResolutionTime/SupportedPerformanceTypes.h>
#include <LibWeb/IndexedDB/IDBFactory.h>
@ -672,7 +673,7 @@ i32 WindowOrWorkerGlobalScopeMixin::run_timer_initialization_steps(TimerHandler
// 13. Set uniqueHandle to the result of running steps after a timeout given global, "setTimeout/setInterval",
// timeout, and completionStep.
// FIXME: run_steps_after_a_timeout() needs to be updated to return a unique internal value that can be used here.
run_steps_after_a_timeout_impl(timeout, move(completion_step), id);
run_steps_after_a_timeout_impl(timeout, move(completion_step), id, repeat);
// FIXME: 14. Set global's map of setTimeout and setInterval IDs[id] to uniqueHandle.
@ -1074,20 +1075,29 @@ WindowOrWorkerGlobalScopeMixin::AffectedAnyWebSockets WindowOrWorkerGlobalScopeM
// https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#run-steps-after-a-timeout
void WindowOrWorkerGlobalScopeMixin::run_steps_after_a_timeout(i32 timeout, Function<void()> completion_step)
{
return run_steps_after_a_timeout_impl(timeout, move(completion_step));
return run_steps_after_a_timeout_impl(timeout, move(completion_step), {}, Repeat::No);
}
void WindowOrWorkerGlobalScopeMixin::run_steps_after_a_timeout_impl(i32 timeout, Function<void()> completion_step, Optional<i32> timer_key)
void WindowOrWorkerGlobalScopeMixin::run_steps_after_a_timeout_impl(i32 timeout, Function<void()> completion_step, Optional<i32> timer_key, Repeat repeat)
{
// 1. Assert: if timerKey is given, then the caller of this algorithm is the timer initialization steps. (Other specifications must not pass timerKey.)
// Note: This is enforced by the caller.
// 2. If timerKey is not given, then set it to a new unique non-numeric value.
if (!timer_key.has_value())
// NB: We deviate from the spec here slightly by reusing existing timers if a timer_key is provided.
GC::Ptr<Timer> existing_timer;
if (timer_key.has_value()) {
auto result = m_timers.get(timer_key.value());
if (result.has_value()) {
existing_timer = result.value().ptr();
existing_timer->set_callback(move(completion_step));
}
} else {
// 2. If timerKey is not given, then set it to a new unique non-numeric value.
timer_key = m_timer_id_allocator.allocate();
}
// FIXME: 3. Let startTime be the current high resolution time given global.
auto timer = Timer::create(this_impl(), timeout, move(completion_step), timer_key.value());
auto timer = existing_timer ? GC::Ref { *existing_timer } : Timer::create(this_impl(), timeout, move(completion_step), timer_key.value(), repeat == Repeat::Yes ? Timer::Repeating::Yes : Timer::Repeating::No);
// FIXME: 4. Set global's map of active timers[timerKey] to startTime plus milliseconds.
m_timers.set(timer_key.value(), timer);